In my prior U.S. Pat. No. 3,782,805, a transparent front projection screen is disclosed and claimed which efficiently uses the light provided by a projector but does not reflect undesirable images to the audience and is viewable from positions other than directly in front of the screen. The projection screen thus taught has proved to be extremely significant and has demonstrated remarkable results with respect to the ability to reflect back to an audience only light incident upon the screen from a small predetermined horizontal angle, while permitting light from outside that horizontal angle to pass therethrough. My U.S. Pat. No. 3,966,301 discloses a screen similar to the one described in my prior U.S. Pat. No. 3,782,805, but has the additional feature of flat portions on the back surface thereof in areas not employed for reflecting light to pass additional ambient light from the preferred horizontal angular direction but falling outside of a preferred vertical number of directions. This screen is an improvement on the screen described and claimed in my prior U.S. Pat. No. 3,782,805 with regard to rejection of non-wanted ambient light.
It has been found that a further source of unwanted reflection due to ambient light results from reflections from the front surface of the transparent screens referred to in the above-mentioned patent and patent applications. While approximately 92% of either projected or ambient light which impinges on the front surface of the screen penetrate that surface and are dealt with by the back surfaces discussed in detail in my above-mentioned patent and patent application, about 8% is reflected by the front surface thereof. This phenomonon referred to as front face reflection, produces an objectionable glare based upon projected light alone to a viewer situated in a position which falls on a line which extends between the surface of the screen and the projection lens. The glare from the projected light will appear as a vertical line on the screen.
It should be appreciated that in a well-lighted room, the front face reflection from ambient light, while being only 8% of the light incident upon the screen, can have a high power content compared with the projected light.
U.S. Pat. No. 2,974,564, which issued Mar. 14, 1961, to W. S. Miller and is entitled PROJECTION SYSTEMS, discloses a system for eliminating glare from front face reflection of a coated screen in which a front projection screen having a transparent front surface coating has reflecting surfaces spaced therebehind which are inclined or tilted with respect to the flat transparent front surface.
Since the front surface of the Miller screen is flat, the screen itself is mounted so that the front surface is included or tilted with respect to the viewing area thus deflecting the glare reflected from the front face into a non-viewing area. The tilt of the projection screen is arranged so that the reflecting surfaces are canted with respect to the projected light to provide the projected image in the viewing area. Therefore, the projector must be in an area other than by the viewing area and the tilted reflecting surfaces project the light into the viewing area. As a result of the tilting of the screen, the tilted reflecting surfaces require intricate and unusual shapes in order to obtain equal intensity across the face of the screen.
A major disadvantage of the Miller system which is a result of the tilting thereof, is the large area required to create a suitable viewing area free of front face reflection, including the area required for the screen, as well as the separate area required for the projector.